This story starts, as others have before it, with a walk around campus during an otherwise regular work day. The ground treasure that caught my eye this time was a dead, but externally undamaged, insect with widely separated eyes, a green and brown body, and clear colourless wings supported by small black fibers running through them. I’m totally ill equipped to identify this specimen so I will pass that responsibility on to you. What species is this? It’s pretty big and I’ve seen a couple on the ground in Philadelphia in the last couple of weeks so it can’t be too obscure. The Academy of Natural Sciences in Philadelphia has an entomology department so I’ll ask someone there and keep you updated on the response. In the mean time, if you recognize this insect, let me know in the comments.

What I’m even more interested in is what I found when I put the wing under an AFM. The surface is densely covered with nanoscale bumps about 150 nm in diameter!

The pattern is regular, in some regions approximating a hexagonal lattice. Are these common features of insect wings? What purpose do they serve? Do the bumps reduce the contact area available for the binding of particles making them easier to dislodge? Does the topography control wettability making a surface that is more hydrophobic than would be possible using smooth waxy excretions alone? Hydrophobicity could be a big advantage for insects that want to fly in the rain or that live around water. A film of water could significantly increase the mass of a very thin wing afterall. Does anyone know, or have other ideas?

The varied morphology of insects is fascinating, but most people, myself included, aren’t aware of the finer structure that can’t be seen by eye or even with an optical microscope. I wonder what else are these incredible material scientists hiding…

It’s a cicada—can’t say what species. The wikipedia entry is a pretty good primer, until your entomology colleagues can fill you in on specifics.

At 150nm, the bumps are starting to approach the size of large biomolecules—they are a little bit too big for single molecules, but aggregates/complexes could reach that size.

I have only one idea you didn’t have already, but it doesn’t seem very likely to me: cicadas use their wings as secondary sound production organs (secondary, that is, to the tymbals). The bumps might provide friction or some other structural quality important for sound generation.

Thanks for the tip. I went to the Wikipedia entry and as I feared, they were described as “one of the most widely recognized of all insects.” My only defence is that they don’t live in Newfoundland… as far as I know!

These folks might appreciate your picture:...Cicadas have three different mechanisms for producing their song ranging from specialized tymbal structure to stridulation and simple wing clapping. ...www.insects.org/entophiles/homoptera/homo_006.html

Cicadas stridulate? I thought they just clapped/flicked their wings. Maybe there’s more to the acoustic idea than I thought.

My favourite guess so far is hydrophobicity, though. Those bumps look as though they might form a surface on which water would ball up rather than wetting it: surface tension would keep a tiny ball of water balanced on the tips of the bumps rather than letting it run down into the valleys.

I can’t image water droplets, but I could make contact angle measurements before and after a treatment of acetone to disrupt the surface (including, of course, AFM imaging to monitor the affects of the acetone). Could be interesting. Maybe I’ll have to find another cicada!

Insect wings are, I think, made primarily of chitin—I don’t know how much protein is also present. Acetone will denature protein, and probably won’t do chitin (a polysaccharide, similar to cellulose) much good either. If the epicuticle (see wikipedia again) extends over the wing surface—as one of the papers below indicates—then the outermost layer is hydrocarbon, which will probably also be stripped by acetone.

Turns out that insect wings have been fairly well studied, because insect flight is not well understood. Here are a few papers that look like a good starting point:

In your defense, you are not the only person who cannot immediately recognize a cicada. I recall an occasion in the NY subway, when I saw a knot of people fearfully exclaiming, “Eeuuw, what is it? Kill it! Kill it!” Curious, I approached and found them surrounding a cicada. So I simply scooped it up and kept walking, hearing behind me horrified cries of “Eeuuw, he touched it!” Cicadas, despite their imposing appearance, are harmless, and I think they are quite beautiful. I simply carried it with me, buzzing loudly, until I was able to release it. It was the only time I’ve seen a cicada as far north as NY. In Houston, where I grew up, the trees at night are buzzing loudly with them.

Could it be to do with turbulence reduction and aiding flight? Maybe air behaves more like a liquid when you’ve got such light wings trying to power through it and (like shark skins) the nanoscale bumps (nice phrase) smooth the airflow.

Oops, I [thought I] posted a link in #3 to a web page of insect, including cicada, photographs; was it deleted? is it invisible? anyhow, I do think yours would be welcome additions to such online compilations if you’ll offer them.

I was also wondering about that but I think the bumps in this case are too small compared to the scale of the wing to have an effect on the turbulence but if you know about aerodynamics please correct me.

Hank:

The link is there in text form. The site looks pretty good but I don’t know that they would be interested in my images. If they were, I would offer them provided they remained free to use.

Hi my name is Milagros Matthews new orlean today i saw this bug like the one on you picture out side of the door and i did nkow what was it so i took a Broom and i move it it was very loudly sound. i want to know if that bug bite and tell me the sign of it.

...I was examining the chitin shells of insects under my microscope in the summer of 1988 along with their pinnate antennae, the fish-scale microstructure of butterfly wings, iridescent colors, and other inventions of nature. I became interested in an amazingly rhythmical microstructure of one large insect detail. It was an extremely well-ordered composition, as though stamped out by factory equipment according to special blueprints and calculations. As I saw it, the intricate sponginess was clearly unnecessary either for the strength of the part, or for its decoration. I have never observed anything like this unusual micro-ornament either in nature, in technology, or in art. Because its structure is three-dimensional, I have been unable to capture it in a drawing so far, or a photograph. Why does an insect need it? Besides, other than in flight, this structure at the bottom of the wing case is always hidden from the eye. No one would ever see it properly. Was it perhaps the wave emitter using “my” multiple cavity structures effect? That truly lucky summer, there were very many insects of this species and I would capture them at night. I was not able to observe these insects neither before, nor later.
I placed the small, concave chitin plate on the microscope stage in order to again examine its strangely star-shaped cells under strong magnification. I again admired this masterpiece jewelwork of nature. I was about to place a second identical plate with the same unusual cell structure on its underside almost purposelesly on top of the first one. But then!
The little plate came loose from my tweezers, hung suspended above the other plate on the microscope stage for a few seconds, then turned a few degrees clockwise and slid to the right, then turned counterclockwise and swung and only then it abruptly fell on the desk.
You can imagine what I felt at that moment. When I came to my senses, I tied a few panels together with a wire and it wasn’t an easy thing to do. I succeeded only when I positioned them vertically. What I got was a multi-layered chitin block and I placed it on the desk. Even a relatively large object, such as a thumbtack, would not fall on it. Something pushed it up and aside. When I attached the tack on top of the “block”, I witnessed incredible, impossible things. The tack would dissapear from sight for a few moments. That was when I have realized that this was no “beacon,” but something entirely different.

Have you ever seen the structure of a fly rostrum? or the intensity of the colours in the wings of Calliphoridae sp, flies are the most exciting creatures, take a little look of their bodies parts and rareties, you will find some interisting physical adaptations on flies, who leads to uncommon features into a common insect.

I sense, as with Peter McGrath, that it could be an aerodynamic aid, especially when you think of the fact it is operating in ultra low Reynolds numbers. The surface could be, depending on the rate of motion and frequency of the wings movement, operating like the surface of a golf ball with all it’s dimples. Pimples have a similar effect. It could possibly work if the wing bends into a convex on the downward flap action. All this assuming there is no other type of epicuticle layer separating the air molecules from this hexagonal surface matrix. Humans are beginning to take more interest in the flight characteristics of animal ornithopters and insecta. The surface, I agree with the previous statement, could be used for sound production also. There is certainly going to be some interesting boundary layer effect. If only you could see the wing move within the viscous relativity at such high magnification and at extremely slow speeds.

2 of my children and i were sitting outside on a hot Sunday morning while my son walked along the brick landscaping around our front porch when he pointed out this extremely large green insect that at first startled me a bit, but upon inspection, it was latched onto a cacoon type of thing…well really it looked like the shell of another insect, brown all-over without wings. My children and I were just curious as to whether this winged insect actually came out of this cacoon-like shell. Thanks from Indiana

Interesting – perhaps the question is not, what are they for, but, why are they 150 nm? Hydrophobicity is a possible reason but I don’t think you need features so small to make a surface hydrophobic. There have been some experiments on this with etched silicon that you might search out. Also, 150 nm is a bit small to be a light-manipulating feature when light is around 500 nm wavelength. I suspect the biological world is crawling (no pun intended!) with such structures that we have yet to discover and explain.

Came across your site while gathering property data on cicadas for work on bio-inspired wings at the University of Florida. I investigate flapping wing performance on the scale of hummingbirds mainly, however many similar principles apply to cicada’s. As many have hypothesized, these structures probably have an aerodynamic benefit. While small, the cicadas fly at Reynolds numbers low enough for them to have an effect on the aerodynamics since you can imagine these wings as, to some extent, swimming through the air. Such bumpy structures help keep the turbulent flow attached to the wing as it performs fairly drastic maneuvers. If the flow separated, it would cause a dramatic increase in drag and decrease in lift (not a good thing if you’re hoping to fly). So in summary, while there are other larger structures on the cicada wing capable of tripping the flow turbulent, these probably help keep it attached.

Having a hydrophobic wing would also be very beneficial since any added mass on a wing beating at 40Hz ish would definitely hurt the cicada’s efficiency!

My question is specifically how small or large do these need to be to have an effect on the flow without causing excessive drag as well as to maintain a hydrophobic wing. If anyone does research determining a range on that please let me know!

I believe the insect you are looking for is called a Cicadas and is primarily in the midwest and its cycle is from 13 to 17 years under ground, the cycle is always a prime number and the reason for this,is so that prediters can not get to them….for example the prediter cycle is ever 4 years. We hope this is the answer to yo0ur search! Please let me know if this helps you because we have this insects in our region and see them and hear them all the time lol!